Our long-term goals are to understand the mechanisms of action of general anesthetics on synaptic transmission. Understanding the mechanisms of both the therapeutic and undesired effects of existing general anesthetics will facilitate safe and appropriate clinical use while enabling rational development of more specific agents with reduced side-effects. Our hypothesis is that general anesthetics affect neurotransmitter release by agent-specific and transmitter-specific presynaptic mechanisms. The major goals will be accomplished by combining neurochemical and novel neurophysiological approaches outlined in the following proposed Specific Aims: 1) Determine the mechanisms by which volatile anesthetics inhibit transmitter release by characterizing both membrane delimited (e.g. ion channel or receptor mediated) and intracellular (e.g. involving fusion/exocytosis machinery) mechanisms of presynaptic general anesthetic effects. The involvement of presynaptic voltage-gated ion channels, ligand-gated ion channels, and vesicle fusion proteins as targets for anesthetics will be assessed. 2) Determine the electrophysiological effects of general anesthetics on presynaptic ion channels using whole-terminal patch clamp recording techniques of isolated rat neurohypophysial nerve terminals. 3) Elucidate transmitter-specific and brain region-specific effects of anesthetics on neurotransmitter release. Neurochemical techniques will be used to determine whether inhibition of glutamate release by general anesthetics in rat cortical nerve terminals can be generalized to other CNS regions and to other transmitter classes. The proposed experiments employ nerve terminals isolated form various regions of the rat CNS to study presynaptic anesthetic effects in a subcellular fraction that is free of intercellular interactions and amenable to pharmacological and electrophysiological analysis. Methods to be used include neurochemical analysis of the effects of representative intravenous and volatile anesthetics on spontaneous and evoked release of endogenous and radiolabeled transmitters and electrophysiological recordings of presynaptic ion channels in isolated nerve terminals. Elucidation of the presynaptic effects of general anesthetics and their mechanisms is essential to understanding the molecular and cellular actions of this clinically important class of drugs on neuronal function.